Method of preparing an adhesive



Patented June 27, 1939 UNITED STATES METHOD OF PREPARING AN ADHESIVEAlexander D. Macdonald, Maiden, Mass., assignor to B. B. Chemical 00.,Boston, Mass., a. corporation of Massachusetts No Drawing. Originalapplication November 22,

1935, SerialNo. 51,114. Divided and this application April 23,1937,

3 Claims.

This invention relates to a method of preparing liquid adhesivecompositions embodying plastic polymerized chloroprene and moreparticularly to such adhesives advantageous for securing togetherleather and shoe parts.

Plastic polymerized chloroprene is chloroprene (also known aschloro-2-butadiene-1,3) which has been partially polymerized, and isplastic in the sense that it may be worked on the rolls of a rubber milland compounded with other ingredients in a manner similar to that inwhich crude rubber is treated. .Such plastic polymerized chloroprene maybe cured or vulcanized to a condition in which it is elastic rather thanplastic, and in which condition itresembles vulcanized rubber. Thiscuring is probably a, further polymerization of the partiallypolymerized chloroprene to a substantially fully polymerized conditionrather than the addition of sulphur to the polymer, such as isconsidered to occur in the vulcanization of rubber.

This is a division of my copending application, Serial No. 51,114, filedNovember 22, 1935, wherein is disclosed a liquid adhesive compositionembodying plastic polymerized chloroprene dispersed or colloidallydissolved in an organic solvent and containing also compounding andcuring ingredients.

In order to obtain optimum results in brushing such liquid adhesive byhand on leather or other material, I have found that the viscosity ofthe liquid adhesive solution should be within the range of from 15 to 25seconds, and preferably from 1'7 to 22 seconds. Where the adhesive is tobe applied by extrusion or other mechanical means, the viscosity of theadhesive may be higher, and up to, for example, seconds. While theviscosity might be expressed in other units, the viscosity is referredto herein in terms of the number of seconds required for a steel ball of9.5 millimeters inch) diameter and weighing from 3.45 to 3.55 grams todrop 40 centimeters through a sample of the liquid adhesive maintainedat 25 C. in a glass tube of 19 millimeters inside diameter.

Due to variability in the constituent materials of the composition, modeof preparation of the composition, and the like, it sometimes happensthat the viscosity of the solution is higher than the above-indicatedrange. The viscosity may, of course, be lowered by the addition of arelatively large amount of solvent but in such case the concentration ofplastic polymer is appreciably lowered, which in many instances isundesirable.

In view of the above considerations, an object Serial No. 138,631

of the invention is to provide an improved method of adjusting theviscosity of a liquid adhesive composition embodying the plasticpolymerized chloroprene. Another object is to provide a method ofreducing the viscosity of such a composition without substantiallychanging a ratio of solids content to solvent.

In the pursuance of the above and other objects I have found that theviscosity of a plastic polymerized chloroprene liquid composition may beregulated'and reduced without substantially affecting the ratio ofsolids to solvent by adding to the composition a small quantity of analcohol. Thus, for example, a cement having a composition similar tothat in the specific example given hereinafter and having a viscosity ofabout 30 seconds may be reduced in viscosity to about 20 seconds by theaddition of about 30 cubic centimeters of ethyl alcohol to a liter ofcement, a reduction in viscosity quite disproportionate to the quantityof alcohol added.

The addition of the alcohol not only effects a reduction in theviscosity of the adhesive but also imparts thereto a smooth andfree-flowing characteristic whereby the cement may be more readilyspread over a surface to which it is to be applied. In another aspect,therefore, the invention contemplates the production of a plasticpolymerized chloroprene liquid adhesive of improved flowing andspreading properties.

I have found to be efficacious for the purpose of this invention methylalcohol, ethyl alcohol, iso-proyl alcohol and butyl alcohol, all ofwhich are monohydroxy alcohols; glycerine, which is apolyhydroxyalcohol; diacetone alcohol, which is a ketoxy alcohol; butylcarbitol, butyl cellosolve, diethylene glycol, and methyl cellosolve,all of which are alkoxy alcohols. I have further found that meta cresol,beta naphthol, resorcinol and phenol function in a manner similar tothat of the alcohols mentioned above with respect to their viscosityreducing effect in the adhesive composition. Hence, in the specificationand claims the term alcohol is used in a generic sense to include all ofthe above-designated compounds. Of the above and other equivalentcompositions, ethyl alcohol is at present the preferred alcohol for usein producing the desired viscosityreducing effect in the adhesivecomposition.

In reducing the viscosity of the liquid adhesive by means of an alcohol,for example ethyl alcohol, the alcohol may, if desired, be addeddirectly to the composition, provided that such direct addition be madecarefully and in small increments so as not to produce local coagulationof the plastic polymer of chloroprene. However. in order to prevent anypossible local coagulation of the pisstic polymer and to make itunnecessary to add the alcohol in small increments, it is preferred toadd the alcohol mixed with one or more of the solvents employed in thecomposition, namely, benzene or trichloroethylene. Thus, a mixture ofequal volumes of alcohol and benzene or trichloroethylene may be addedmore freely to the liquid adhesive to produce the desired reduction inviscosity and without danger of local coagulation of the dissolvedmaterial. This latter feature is of particular interest where the ratioof solids to solvent is such that the incorporation of additionalsolvent is feasible or desirable, the result being a reduction inviscosity far greater than would be accomplished by the addition of thesolvent alone or than would be expected by the addition of a merediluent.

An example of a composition in connection with which this invention maybe practised is as follows:

. Grams Plastic polymerized chloroprene (containing 2%pheneyl-beta-naphthylamine) 900 Wood rosin (FF) 45 Magnesium oxide(light calcined) 90 Zinc oxid 45 Phenyl-beta-naphthylamine(stabilizer)--- 9 Benzene 1890 Trichloroethylene..., 2850 Sulphur 27 DuPont Accelerator #808 (butyraldehyde aniline condensation product) ,Itis to be noted that i this example the hentic polymer is milled on arubber mill and the wood rosin, magnesium oxide and zinc oxide are addedduring the milling, preferably in that or-: der. The resultant milledsolid polymer is then cut up into small pieces and is added in a churnto a mixture of the benzene and trichloroethylene.

The phenyl-beta-naphthylamine is also added in the churn. When theresulting solution of the milled material in the solvent hasbecomesufflciently viscous to support the sulphur in suspension during theagitation of the solution, the sulphur is introduced into the solutionand the agitation thereof is continued until the sulphur has beendispersed or dissolved.

The accelerator preferably is added not more than 24 hours prior to theactual use of the liquid solution for adhesive purposes. It isconvenient to withhold a portion of the solvent and to dissolve theaccelerator therein, and then to add the accelerator solution to thecomposition.

In the above composition the plastic polymerized chloroprene is ofcourse the adhesive material. The wood rosin is a softener for the pisstic polymer of chloroprene and it assists also in the curing of thepolymer. Abietic acid, which is the major constituent of wood rosin, maybe substituted for all or a part of the wood rosin. The

' magnesium oxide serves to neutralize any hydrochloric acid which maybe set free in the polymerized chloroprene, and to prevent scorchingwhen the zinc oxide and plastic polymer of chloroprene are milledtogether. Light calcined magnesium oxide is preferred because of thegenerally better results to be obtained therewith.

The zinc oxide appears to assist in the curin or more completepolymerization of the plastic polymer of chloroprene. Thephenyl-beta-naphthylamine functions as a stabilizer to inhibit prematurecuring of the polymer. The sulphur assists in the curing orvulcanization of the plastic polymer and appears to contribute toimproved properties of the resulting adhesive bond. The acceleratorserves to initiate the rapid curing or completion of the polymerizationof the plastic polymer at temperatures in the neighborhood of roomtemperature, and thus making unnecessary heating the parts to be joined,for example shoe parts, to high vulcanizing temperatures. In cases whererapid curing of the polymer is not necessary or desirable, or where itis feasible to employ heat to bring about the cure, the accelerator maybe omitted.

While the volume ratio of benzene and trichloroethylene is preferably1:1, said ratio may satisfactorly vary from 1:2 to 2:1. Theconcentration of plastic polymerized chloroprene may be varied fromabout 1% to about 2%, pounds of plastic polymer to the gallon ofsolvent. A composition wherein the concentration of plastic polymerizedchloroprene varied from about 1% to 2 pounds of plastic polymer pergallon of solvent and wherein the solvent blend ratio of benzene andtrichloroethylene ranged from 1:2 to 2:1 by volume, would comprise inparts by weight, 1 part of plastic polymerized chloroprene, 1 to 3 partsby weight of benzene, and 5% to 2 parts of trichloroethylene, or, interms of total solvent, 1 part plastic polymer and 4 to '1 parts ofsolvent blend.

The incorporation of the alcohol into the composition for the purposesof this invention may be carried out by adding the alcohol directly tothe composition. In such case the alcohol should be added carefully andin small increments so as not to produce local coagulation of theplastic polymer of chloroprene. Where the addition of more solvent isfeasible the alcohol may be mixed with the solvent and then added to thecomposition. Thus, in the compositiongiven above a mixture of equalvolumes of alcohol and benzene or trichloroethylene may be added morefreely than alcohol alone to produce the desired reduction in viscosityand without danger of local coagulation of the dissolved or dispersedmaterial. It will be understood, of course, that the reduction ofviscosity of the liquid adhesive by means of an alcohol is not limitedto compositions embodying benzene and trlchloroethylene but may beemployed with other solvents for plastic polymerized chloroprene.

In preparing a liquid cement of predetermined viscosity from plastic Ipolymerized chloroprene and compounding ingredients, the polymertogether with the compounding ingredients may be dissolved or dispersedin an amount of solvent less than suiilcent to impart the desiredviscosity to the resulting solution. The solution may then be broughtdown to the desired viscosity without any coagulation of dissolved ordispersed ingredients by adding a mixture 01' an alcohol and a sol-,vent for the polymer. The solid content of the resulting composition ishigher than would be the case if the viscosity had been reduced withsolvent alone, with the attendant advantage that when the composition isemployed for adhesive purposes, a larger quantity of solids may bedeposited from a given volume of liquid adhesive composition. Moreover,the presence of the alcohol imparts smooth and free-flowingcharacteristics to the composition whereby it may be more readily spreadover a surface to which it is v to be applied. In carrying out theadhesion of leather or shoe parts by means of the liquid adhesivecomposition of this invention, the leather parts are preferably firstroughed in a suitable manner, such as by an emery wheel or a wire brush,in order to provide surfaces most advantageous for cementing. The liquidadhesive is then applied, preferably to both surfaces to be united. Theapplication of the adhesive may be by brush, by extrusion, or in anyother suitable manner. The applied composition is then permitted to dryfor a sufli'cient length of time to remove a major portion of thesolvent. At the time of the application of the adhesive to the leatherthe leather may be water-moistened, or, as known in the art, intemper.However, where conditions permit, it is desirable, though not necessary,to have the leather in an air-dry condition. Ordinarily a drying time ofnot more than about one hour is necessary before the adhesive coatedparts may be brought together under attaching pressure. Onthe otherhand, the adhesive may be permitted to dry for as much as 8 hours beforebringing the adhesive coated parts together without seriously affectingthe strength of bond. After asuitable drying period as described above,the parts are brought together .under attaching pressure, eithermomentarily or for a longer period. By way of example, in the adhesiveattaching of shoe parts an attaching pressure of 80 pounds'per squareinch has been found satisfactory. Lower attaching pressures may beemployed but preferably a relatively high attaching pressure is used.

Having described my invention, what I claim as new and desire to secureby Letters Patent of the United States is:

1. The method of preparing a liquid vulcanizable cement from plasticpolymerized 'chloroprene and' compounding ingredients and having aviscosity such that it may be readily spread over a surface to which itis to be applied which comprises dissolving the polymer together withthe compounding ingredients in an amount of solvent and compoundingingredients and having a viscosity such that it may be readily spreadover a surface to which it is to be applied which comprises dissolvingthe polymer together with the compounding ingredients in a solvent, andsubsequently adding an alcohol thereto in small increments, therebysubstantially reducing the viscosity of the solution without anycoagulation of the dissolved ingredients.

3. The method of preparing a liquid vulcanizable-cement from plasticpolymerized chloroprene and compounding ingredients and having aviscosity such that it may be readily spread over a surface to which itis to be applied which comprises dissolving the polymer together withthe compounding ingredients in an amount of solventdess than suflicientto impart the desired viscosity to the resulting solution and adding tothe solution a mixture of a solvent for said polymer and ethyl alcohol,thereby substantially reducing the viscosity of the solution without anycoagulation of the dissolved ingredients.

ALEXANDER D. MACDONALD.

